COVID-19 and influenza: how do they compare?


There has been considerable admonishment from both public health authorities and the media that we should not speak of COVID-19 as ‘just another flu’.

It’s far worse than that, according to science blogs with titles such as ’13 Coronavirus myths busted by science’, which insist that “COVID-19 has a mortality rate more than 20 times higher [than influenza].”

According to the World Health Organization (WHO), the symptoms of the newly-named disease attributed to SARS-CoV-2 infection are virtually indistinguishable from those of influenza:

“COVID-19 and influenza viruses have a similar disease presentation. That is, they both cause respiratory disease, which presents as a wide range of illness from asymptomatic or mild through to severe disease and death.”

What is even more important is that most cases of acute respiratory illness that are lumped into the category of influenza or ‘flu’ are in fact influenza-like illness rather than ‘true’ influenza – that is, they are caused by respiratory pathogens other than influenza viruses, but the illnesses caused by the various different respiratory tract viruses are clinically almost indistinguishable from each other:

“A reliable clinical diagnosis of influenza can be difficult, due to the variability of its presentation. There is also a multitude of other respiratory viruses in both children and adults which may cause a similar constellation of symptoms.”

As veteran influenza researcher, British epidemiologist Tom Jefferson explains,

“[Influenza] is a syndrome, there is not a single cause, and the gallery of “culprits” increases as time goes on. But it is mysterious, it comes and goes. That is why it is called influenza, as our forefathers ascribed its waxing and waning to the influenza degli astri, or “influence of the planets.” Meaning they had not a clue as to where and how it started and where it went. We are still clueless.”

Influenza-like illness (ILI) is defined by the WHO as an acute respiratory infection with a cough, measured fever of 38°C or above, and with onset within the last 10 days.

Under normal circumstances, people who present for medical care with these symptoms are not routinely tested to determine which virus (or other respiratory pathogen) they’re infected with, since the general treatment advice is the same.

However, the US Centers for Disease Control (CDC) Influenza Surveillance System analyses samples taken from people with ILI at approximately 100 public health and over 300 clinical laboratories located throughout the US and its territories, in order to monitor influenza activity throughout flu season.

Their cumulative data from the current flu season demonstrate that only around one fifth of people who have developed ILI have been found to be infected with influenza viruses.

The remaining sufferers of ILI are infected with a wide variety of respiratory pathogens, including the four coronaviruses that are already endemic in human populations.

Just two of these commonly-circulating coronaviruses infect up to 26% of the population each year and are found in up to 12% of people who are hospitalised for a respiratory tract infection.

The widely-circulating OC43 strain of coronavirus caused an outbreak of severe respiratory diseasewhich affected 67% of the residents and 33% of staff members in a Canadian nursing home in 2003; 12% of the 142 residents developed pneumonia and 8 died, 6 of pneumonia. No staff member developed pneumonia or died.

This case fatality rate of 8% among the elderly residents of the Canadian nursing home, from an endemic coronavirus that caused nothing more than common cold symptoms in staff members, is exactly the same as the 8% case fatality rate in people aged 70-79 observed in the first case report on the outbreak in China.

In a study of patients with chronic obstructive pulmonary disease, 14% of patients who suffered influenza-like illness were actually infected with coronaviruses, not influenza viruses.

World-renowned epidemiologist Professor John Ioannidis sums it up well:

“Different coronaviruses actually infect millions of people every year, and they are common especially in the elderly and in hospitalized patients with respiratory illness in the winter…
Leaving the well-known and highly lethal SARS and MERS coronaviruses aside, other coronaviruses probably have infected millions of people and have killed thousands. However, it is only this year that every single case and every single death gets red alert broadcasting in the news.”

With that as context, let’s look at some numbers, to gain a sense of perspective on the disproportionate amount of attention that has been paid to COVID-19 in comparison to influenza and ILI:

Worldwide, the World Health Organization estimates that seasonal influenza causes about 290 000 to 650 000 deaths per year (COVID-19 so far: 125 951 deaths, with evidence of substantial overcounting due to conflating of ‘deaths with’ and ‘deaths from’ SARS-CoV-2 infection).

The United States Centers for Disease Control (CDC) estimates that in the current flu season (starting 1 October 2019, last update 4 April 2020),

  • 39 000 000 – 56 000 000 people have developed influenza
  • 410 000 – 740 000 have been hospitalised for influenza
  • 24 000 – 62 000 people have died from influenza (COVID-19: 25 856 deaths so far, again with evidence of substantial overcounting).

(Note the wide range of estimates; this is because, as explained above, people with ILI are not routinely tested to see if they actually harbour influenza viruses and “influenza is not a reportable disease in most areas of the United States”; hence, as John Ioannidis points out, “some of these deaths are due to influenza and some to other viruses, like common-cold coronaviruses.”)

In Italy, influenza is estimated to have led to 24 981 excess deaths (that is, deaths above what would normally be expected in that population) during the 2016/17 flu season. (COVID-19: 21 067 deaths so far but remember Professor Walter Ricciardi, scientific adviser to Italy’s minister of health, has acknowledged that “The way in which we code deaths in our country is very generous in the sense that all the people who die in hospitals with the coronavirus are deemed to be dying of the coronavirus. On re-evaluation by the National Institute of Health, only 12 per cent of death certificates have shown a direct causality from coronavirus.”)

In England, during recent winters there have been about 17000 excess deaths from flu per year. (COVID-19: 12 107 deaths so far, again with evidence of substantial overcounting.)

In Australia, each year, on average, influenza causes

Many epidemiologists who are intimately familiar with the burden of disease and death from ILI have expressed their bewilderment at the disproportionate reaction to the emergence of a novel coronavirus that causes ILI.

John Ioannidis wrote, with evident frustration at the media circus,

“If we had not known about a new virus out there, and had not checked individuals with PCR tests, the number of total deaths due to “influenza-like illness” would not seem unusual this year. At most, we might have casually noted that flu this season seems to be a bit worse than average. The media coverage would have been less than for an NBA game between the two most indifferent teams.”

Similarly, Tom Jefferson, who has been immersed in the study of ILI for decades as an author of Cochrane reviews on influenza vaccination, surmises that

“The data support the theory that the current epidemic is a late seasonal effect in the Northern Hemisphere on the back of a mild ILI season. The age structure of those most affected does not fit the evidence from previous pandemics.” [That is, historical pandemics have “cause[d] excess mortality in ‘unusually young populations‘ whereas COVID-19 is causing the same mortality pattern as regular seasonal flu, with over 90% of deaths occurring in people aged 65 and over.]

The Italian health ministry has also noted that the 2019/20 flu season was unusually mild compared to previous years, which left many frail, sick elderly people who would normally have succumbed to the flu, alive and susceptible to COVID-19.

Circling back to the claim that ‘COVID-19 is 20 times deadlier than the flu’, the case fatality rate (CFR) for seasonal influenza is generally held to be around 0.1% (that is, 1 out every 1000 people diagnosed with influenza will die), while the 1918 Spanish flu had a CFR of above 2.5% (that is, more 25 out every 1000 people diagnosed with Spanish flu died).

As the Oxford COVID-19 Evidence Service points out,

“Evaluating CFR during a pandemic is… a very hazardous exercise”

because of selection bias (people with symptoms are far more likely to be tested than asymptomatic people), differences in testing rates between countries and even regions within countries, inconsistencies between definitions of cases in different regions, differences in patient demographics and burden of comorbid diseases, and differences in the attribution of deaths (dying with the disease – association – vs dying from the disease – causation.

Accordingly, estimates of the CFR for COVID-19 range from 2.3% in the initial case series reported in China, dropping to to 0.7% for patients with symptom onset after 1 February; 0.85% on the Diamond Princess cruise ship (among an elderly population in whom the CFR would be expected to be high), all the way down to 0.21% in Iceland.

While the CFR is a measure of how many people who have been diagnosed with an illness end up dying, infection fatality rate (IFR) is a measure of how many people who have been infected with a pathogen – including those who have no symptoms or have symptoms but are not diagnosed – end up dying.

It is now apparent that SARS-CoV-2 has been spreading through the populations of many countries, largely silently, reaching infection rates of up to 19% in Wuhan, China and 15% in the German municipality of Gangelt. Since up to 80% of people infected with SARS-CoV-2 have no symptoms, the infection fatality rate is considerably lower than the case fatality rate, with estimates ranging from between 0.01% and 0.19% in Iceland, to 0.37% in Gangelt, Germany, to 0.9% in the UK.

The Oxford COVID-19 Evidence Service concludes that:

“Taking account of historical experience, trends in the data, increased number of infections in the population at largest, and potential impact of misclassification of deaths gives a presumed estimate for the COVID-19 IFR somewhere between 0.1% and 0.36%.”

The IFR in Wuhan City, which has experienced widespread community transmission of SARS-CoV-2 and therefore can be expected to have already developed significant herd immunity, is estimated at 0.12%.

Only once widespread antibody testing has been performed will it be possible to accurately estimate the CFR and IFR of SARS-CoV-2, and both these numbers will vary according to demographic and other risk factors in different populations.

The take-home message, however, is that far from COVID-19 being ’20 times more deadly than flu’, as veteran epidemiologist and influenza-like illness specialist Tom Jefferson has mused,

“There does not seem to be anything special about this particular epidemic of influenza-like illness.”

Remember, taking good care of your health is even more important than usual due to the high levels of stress generated by the world’s response to COVID-19, and the fact that people with pre-existing chronic disease, as well as smokers and people with obesity, are at higher risk of serious complications of infection.

If you are overweight or have a chronic disease that puts you at increased risk of serious illness from viral infection, NOW is the time to take action on it! Obesity, type 2 diabetes, hypertension and coronary artery disease are preventable and largely reversible with a wholefood plant-based diet.